The long-term goals of this proposal are to determine the in vivo functions of a protein related to the amyloid precursor protein (APP) during normal development, and to gain insight into how perturbations of these functions may contribute to the pathology of Alzheimer's disease (AD). AD involves the cleavage of beta-amyloid fragments (Abeta) from APP and its subsequent aggregation into dense plaques in the nervous system. Although Abeta itself has neurotoxic effects, APP must play physiological roles that are also disrupted in AD. A variety of studies have suggested that APP may regulate neuronal migration and outgrowth by acting as a transmembrane receptor, possibly via interactions with several intracellular signaling pathways. Particularly compelling are experiments demonstrating that APP695 (considered a neuronal isoform of APP) binds directly to the heterotrimeric G protein Go-alpha and can regulate its activity. However, a functional analysis of these interactions has been precluded by complexities associated with the mammalian nervous system. To address this issue, a model system (the enteric nervous system of Manduca sexta) has been established in which an identified set of migratory neurons (the EP cells) can be visualized and manipulated within the intact nervous system in embryonic culture. These neurons express an APP-like protein (msAPPL) that co-localizes with Go-alpha in their leading processes, and preliminary studies have shown that inhibition of msAPPL expression by the EP cells perturbs their migration in a manner consistent with the disruption of endogenous Go-alpha-mediated signaling events. The goals of this proposal are to investigate the role of msAPPL processing with respect to neuronal migratory behavior, to clarify the nature of msAPPL interactions with Go-alpha, and to determine whether msAPPL acts as a Go-alpha-coupled receptor that regulates neuronal migration in vivo. These studies will lend new insight into the molecular mechanisms by which APP-related proteins function in the developing nervous system, and they should serve as the foundation for future research into how disruption of these mechanisms contributes to the pathology of AD.